1. Field of the Invention
The present invention relates to a semiconductor device having a circuit in which a thin film transistor (hereinafter referred to as TFT) is formed on a substrate having an insulating surface, and to a manufacturing method thereof. More particularly, the present invention relates to an electro-optical device typically known as a liquid crystal display device provided with an excellent-shaped contact hole, and to electronic equipment with an electro-optical device. Moreover, the semiconductor device according to the present invention refers to all equipment utilizing the semiconductor characteristics for functioning. The above electro-optical device and the electronic equipment with an electro-optical device are also included in semiconductor devices.
2. Description of the Related Art
The development of a semiconductor device having a large-area integrated circuit formed by the TFT (thin film transistor) on its insulating surface is under progression. AN active matrix liquid crystal display device, an EL display device, a contact-type image sensor, and the like are known as representative examples.
The characteristics of the TFT are deteriorated and reliability is lowered when organic resin film is directly formed on the TFT provided on the insulating surface. To solve those problems, conventionally, a laminated organic resin film is formed on the TFT after the formation of an inorganic insulating film (also called passivation film).
The TFT is normally connected to wirings through a contact hole. Therefore, when the above inorganic insulating film is provided on the TFT, it is necessary to form a contact hole for connecting to the upper layer wiring in the inorganic insulating film and the organic resin film which covers a TFT gate electrode, a source electrode, or a drain electrode. For instance, the contact hole is formed for connecting a drain electrode of a pixel TFT with a pixel electrode in an active matrix liquid crystal display using TFT.
A conventional manufacturing process will be described with reference to FIGS. 17A through D. Shown here is an example of an active matrix liquid crystal display applied to this process. Although the pixel TFT is not shown for simplification, a first conductive film 11 is identical with a drain electrode of a pixel TFT or electrically connected thereto. Also not shown is that there is a single layer or a multiple layer of insulating film between a substrate 10 and the first conductive film 11.
Shown in FIG. 17A is a state where the first conductive film 11 identical with the drain electrode of a pixel TFT or electrically connected thereto is formed on the substrate 10 on which the pixel TFT is formed. An inorganic insulating film 12 and an organic resin film 13 formed in laminations are formed on top of the first conductive film 11.
And shown in FIG. 17B is a state where the first patterning is performed by using a resist mask 14 by way of photolithography, and a first contact hole is opened only in the organic resin film 13.
Subsequently, a second patterning is performed by using a resist mask 15 after removing the resist mask 14, and a second contact hole is opened only in the inorganic insulating film 12. This state is shown in FIG. 17C. Since the second contact hole is formed in the bottom portion of the first contact hole, the diameter of its opening is smaller than that of the first contact hole.
Shown in FIG. 17D next is a state where a pixel electrode 16, made of transparent conductive film, is formed after removing the resist mask 15.
As shown in FIG. 17D, in this way there is a step in the shape of the contact hole because it has been formed after the first and second patterning processes.
Additionally, besides the above conventional manufacturing method, another method is to perform patterning right after forming the inorganic insulating film, then form the organic resin film and perform patterning again to form a contact hole. Two patterning processes were also necessary even in this method.
Since the number of processes and masks has increased due to two patterning (organic resin film patterning and inorganic insulating film patterning) processes in the conventional method, this led to an increase in costs.
In the two patterning processes, each method uses different photo mask, and therefore poor contact occurred when the masks had not been overlapped in precision. Also, in the example of the conventional process shown in FIG. 17, fining of the contact hole is difficult. That is because considering the margin when overlapping, the opening diameter of the second contact hole that was opened in the second patterning is 1.5 to 2 times bigger than the opening diameter of the first contact hole opened in the first patterning process.
Furthermore, the shape of a conventional contact hole (of which an example is shown in FIG. 17D) is a complicated shape formed by overlapping two contact holes with different opening diameter. Thus, poor coverage has occurred on a second conductive film formed later.